The overall objective of the proposed research is to establish an active and productive research program which will contribute to a better understanding of the molecular biology of the bovine leukemia virus (BLV), a possible prototype of a New Family of Leukemia viruses. The specific aims are to isolate, purify, and characterize the structural proteins of the BLV (applicant's isolate-BLV/bat2); to prepare high titered monospecific antisera; to determine if any antigenic relationship exists between BLV and other leukemia viruses; to compare various BLV isolates; and to study the mechanism of syncytia induction. Isolation and purification of the BLV proteins will involve gel filtration in the presence of guanidine-HCL, affinity column and ion exchange chromatography, and/or isoelectric focusing. Monospecific sera will be used in the antigenic analysis of the BLV proteins as well as to determine their location in BLV infected cells and tumor tissues. Immunological techniques such as the radioimmunoassay, indirect immunofluorescence test, and the cytotoxicity test will be employed. Isolates of BLV from various laboratories will be compared for syncytia inducing ability, antigenic relatedness, and polypeptide composition. Studies on the mechanism of syncytia induction will be conducted to determine if macromolecular synthesis is required for cell fusion and to determine which, if any, BLV glycoproteins play a role in syncytia induction. Monospecific antisera prepared against the BLV glycoproteins will be used in syncytia inhibition studies to help elucidate the role of specific glycoproteins. The proposed studies on the structural proteins will provide immunological reagents that may be very valuable for studies determining relationships between BLV and other leukemia viruses (including those isolated from man) and the virus gene expression in tumor cells. In addition, the comparison studies on the different BLV isolates may clarify some of the discrepancies that exist in the field of BLV work. It is also possible that there exists more than one strain of BLV and these studies may give suggestive evidence of this.